Conventional cable and satellite television transmission is evolving into interactive television or televideo (IT) systems. IT systems combine the video broadcast capability characteristic of conventional broadcast television with computer-executed applications or programming responsive to input from viewers. By some estimates, IT systems under development could include the equivalent of 500 channels of video broadcasting and unlimited numbers of interactive applications.
Conventional broadcast television networks primarily transmit scheduled video programming that emphasizes entertainment, education, or commercial advertising. The conventional scheduled programming is sometimes interrupted for unscheduled public announcements relating to, for example, broadcast system technical difficulties, critical events, or weather or disaster alerts.
Public announcements in conventional broadcast television systems are broadcast on the channels carrying the scheduled programming. Critical public announcements typically are broadcast as substitutes for the scheduled programming. The broadcasting of the scheduled programming is stopped and in its place the public announcement is broadcast. These substitution-type public announcements commonly are voiced or spoken and include a video segment or a still-image graphic display. This type of public announcement is typically used to announce broadcast system technical difficulties and weather or disaster alerts.
Non-critical public announcements may be generated as text that is added to a video broadcast signal (e.g., along a bottom display screen margin). The broadcasting of the scheduled programming continues uninterrupted, but the broadcast signal carrying the scheduled programming is modified to include the public announcement text. These modification-type public announcements seldom include voice or spoken components and are commonly used to announce non-critical programming delays or news (e.g., sports results).
Typically, public announcements are made by the broadcasters that provide or generate the programming carried on a particular channel. Conventional cable television (CATV) network operators seldom generate such announcements. Conventional CATV network operators are substantially passive rebroadcasters of programming provided or generated by others. As a consequence, viewers of a conventional CATV network typically can receive public announcements only if the viewers are tuned to programming provided by a broadcaster that makes public announcements (e.g., conventional local television stations or national television networks).
With the relatively large amounts of programming planned for IT systems, it is expected that the proportion of viewers tuned to such conventional broadcasters will decline. Much of the alternative programming is likely to be generated by providers who are remote from the viewer or have no public announcement capabilities. With conventional channel-based broadcasting of public announcements, viewers tuned to such programming could be denied the benefit of receiving public announcements. For critical events and local weather or disaster alerts, the absence of public announcement services can pose a grave risk to viewers.
In addition to the difficulty of delivering public announcements to the program or channel a viewer is actually watching, another disadvantage is that public announcements on conventional television are delivered to all viewers tuned to a particular channel. As a consequence, conventional television is incapable of providing a public announcement only to specific viewers for which the announcement is applicable or appropriate.
With particular reference to IT systems, conventional substitutions or modifications of video signals for public announcements is incompatible with programming in the form of computer-executed applications. Many such applications would not include a video broadcast that could be modified with a public announcement. Moreover, public announcements could unpredictably disrupt the operation of such applications.